The present invention relates to rubberless tire bead assemblies and to novel methods of manufacturing such tire bead assemblies to produce a strength efficiency tire bead assemblies which are of the same efficiency as conventional wire tire bead assemblies which include a rubber or polymeric coating thereon.
All automotive tire bead assemblies composed of round wire strengthening elements in general use contain either a thin coating of rubber on the wire surface or contain wire elements embedded in a ribbon or elongate form of rubber, with the single exception being the rubberless cable bead. An important function of the rubber coating around the wire element is to hold the multiple wire wraps together after forming so that the tire bead assembly may be removed from the bead forming machine and handled during the course of the bead assemblies incorporation into the tire during the tire building operation. The necessity for the existence of such an adhesive function of the wire elements becomes increasingly important for stiff, high-strength wires, such as steel, because of their spring-back characteristics. That is, although a wire may be readily and neatly wound on a spool, the wire often becomes entangled upon removal from such a spool because of back tension, wire twist and cast properties of the wire elements. Also, such bead assemblies tend to lose their constructional integrity upon removal from the bead forming drum unless the wire is rubber coated. The cable bead, generally composed of a wrap wire helically wound around a core hoop contains an inherent compressive or resisting force and because of the helical wrap geometry, cable beads require excessive forming times and operations, thereby resulting in a substantially expensive bead assembly.
One deficiency of conventional rubber coated wire tire bead assemblies arises when under the low viscosity or near liquid environment that occurs during final curing of the completed tire, the adhesive nature of the rubber coated wires is substantially reduced and spring-back of the wire elements or other distortion to the original bead geometry may occur.
Furthermore, a limitation to bead geometry is inherent to conventional tire bead assemblies comprised of multiple wraps of rubber ribbon containing more than one wire. Such ribbons must be wound with the ribbon width oriented exactly parallel to the winding axis so as to consume in each wrap of ribbon precisely the same length on each side of the ribbon. This forming requirement prohibits constructions, such as those containing conical geometric form such as would mate with a tire wheel rim having state-of-the-art tapered surfaces of revolution.
A further potential deficiency of state-of-the-art beads in general use is the inherent absence of void space free of rubber internal to the bead wire array.
Additionally, although in conventional round wire tire bead assemblies the rubber bonding or coating thereon facilitates bonding the wires together to provide the resultant tire bead assembly or bundle, the use of a rubber coating on the bead wires to manufacture tire bead assemblies requires a separate rubber making operation and expensive extrusion equipment to effectively produce the thin coating on the wire elements that comprise the tire bead assembly. The resultant reduced speed limitations in manufacturing such tire bead assemblies and the necessity of required overlaps of the wire endings for proper adherence of wire end to bead assembly and the tendency of the wire endings to spring away from the bundle during the tire making processes are problems that are inherent in such rubber-coated tire bead assemblies. Additionally, the high cost of the special formulated rubber coatings results in higher cost tire bead assemblies which, if eliminated, would substantially reduce the time required for manufacturing such tire bead assemblies and would decrease the cost of such manufacture process thereby providing higher speed and greater productivity during the bead making operations.
Prior art attempts to make a rubberless tire bead assemblies include, for example, Lejeune U.S. Pat. No. 3,949,800, Grosch, U.S. Pat. No. 4,216,814, Pfeiffer U.S. Pat. No. 4,290,471, and Mertin, U.S. Pat. No. 4,406,317 patents which disclose a plurality of rectangular-shaped wire elements to make a bead assembly having sharp corners. The resultant rubberless tire bead assemblies exhibit an absence of voids within the bead assemblies and require a special ductile steel material to be positioned around the bead as an integral part of the bead making cycle. Such tire bead assemblies possess sharp corners that adversely effect other materials in the bead are during service, do not contain void reservoirs within the bead assemblies, utilize expensive polygon-shaped wire elements, and require that the bead making cycle is dominated by the time necessary to deform and position steel materials around the bead at numerous locations to retain the bead assembly. Accordingly, such beads have enjoyed little, if any, commercial acceptance.
Additionally a rubberless round wire bead with homogeneous joining of touching or contiguous wires, incorporating joining means such as sintering has been disclosed by Pearce U.S. Pat. No. 3,372,894.
Additionally, the conventional cable bead assembly is a rubberless tire bead assembly which is generally comprised of at least two wire components, a wire wound about a core wire, and a ferrule component for joining the wound wire ends. However, such cable bead assemblies tend to be excessively flexible and prone to bending and require excessive time cycles in manufacturing the bead assembly thereby resulting in increased costs of manufacture. See, for example, Gore U.S. Pat. No. 2,069,525 to such a cable bead assembly.
U.S. Pat. No. 4,039,015 discloses a rubberless bead which may be formed, for example, as the result of interlocking a multiple number of independent hoops with welding or interlocking a multiple number of hoops twisted from a single wire length with welding. However, such constructions are readily distorted due to the helical or nonparallel nature of individual wire axes one to another. Furthermore, the disclosed construction made from a single length of wire contains a relatively large number of wire crossover points which represent points of nonuniform stress distribution under load and potential wear and deformation cites.